1. Field of the Invention
The present invention relates to a hospital bed and more particularly to dual drive mechanisms with respective actuators for selectively raising and lowering either end of a hospital bed.
2. Background of the Invention
Many activities and therapies require that a hospital bed be adjustable to different heights, and/or its ends be inclined relative to a horizontal plane so that either the foot of the bed is elevated above the head of the bed, i.e. the Trendelenburg position, or the head of the bed is elevated above the foot of the bed, i.e. the reverse Trendelenburg position. It is further desirable that the Trendelenburg or reverse Trendelenburg positions be achieved at any height of the bed.
U.S. Pat. No. 4,494,259 discloses one apparatus for controlling the height and inclination of either end of a hospital bed. In that disclosure an actuator drives one or two screw and nut drives which may be connected by a clutch. Engaging the clutch couples the screws causing both screws to rotate in unison. The bed is raised or lowered via a linkage mechanism connected between the bedframe and the nuts. Disengagement of the clutch decouples the screws, and one screw and nut drive is operative to raise or to lower a foot end of the bedframe. Consequently, the Trendelenburg position may be achieved by engaging the clutch, fully lowering the bed, disengaging the clutch and raising the foot end of the bed. The reverse Trendelenburg position is achieved by engaging the clutch, raising the bed, disengaging the clutch and lowering the foot end of the bed. Consequently, to move from the Trendelenburg position to the reverse Trendelenburg position or vice versa, it is often necessary to change the height of the bed before its inclination may be changed.
In view of the fact that hospital bed motion must be very slow to accommodate the sensitivities of a patient, this dual motion is inefficient and requires additional personnel time.